Customers often send us this question on WhatsApp. It is also the one most quotes ignore — and getting it wrong means being sold a system that exceeds your supply limit and needs a paid TNB Connection Confirmation Check (CCC) assessment (RM1,000) before it can be connected.
The short version
Solar ATAP (GP/ST No. 60/2025) caps your system on inverter capacity in kWac, not on panel capacity in kWp, and the cap depends entirely on your supply phase:
| Domestic supply | Maximum inverter | Largest clean system |
|---|---|---|
| Single phase | 5 kWac | 7.44 kWp (12 panels) |
| Three phase | 15 kWac | ~19.84 kWp (32 panels) |
That is a limit under §8.1, not a Trexon preference. Roof space and budget do not change it; going over it requires a paid TNB CCC assessment (RM1,000) and a waiting period, and is not automatic.
Why this decides everything before your bill does
Most sizing conversations start with the electricity bill, and that is the right second question. But if your house is single phase, a bill of RM400 and a bill of RM900 land you in the same place: 7.44 kWp, because that is the ceiling. The bigger bill simply means a larger share of it stays unoffset.
This is why we ask about phase before quoting anything above 7.44 kWp. A sizing tool that does not ask will happily propose an 8 kWac system to a single-phase home. That system exceeds that supply's limit and would need a paid TNB CCC assessment (RM1,000) first; it is not automatic.
How to tell which one you have
- Look at your meter. A single-phase supply has one live conductor plus neutral. A three-phase meter is physically larger and is fed by three lives plus neutral.
- Look at your main breaker (MCCB). Single phase is usually one wide switch; three phase is three switches ganged together, so they trip as one.
- Check the rating. Domestic single phase is commonly 60A or 100A. A three-phase board will state a per-phase rating.
- Or just send us a photo of the meter and main board. It takes us a few seconds and removes the guesswork entirely.
Older terrace houses and most flats are single phase. Larger semi-Ds, bungalows and any house with several air-conditioners or an EV charger are more often three phase — but there is no reliable rule by property type, so check rather than assume.
What each phase can actually take
Every system below runs on a 5 kWac inverter, so all four are legal on a single-phase supply:
| System | Panels | Inverter | Generates (approx) |
|---|---|---|---|
| 5.58 kWp | 9 | 5 kWac | ~586 kWh/month |
| 6.20 kWp | 10 | 5 kWac | ~651 kWh/month |
| 6.82 kWp | 11 | 5 kWac | ~716 kWh/month |
| 7.44 kWp | 12 | 5 kWac | ~781 kWh/month |
Above that, systems step up to 8 kWac and beyond, which requires three phase. Generation assumes 3.5 peak sun hours over 30 days.
If your bill wants more than single phase allows
You have two honest options, and we will not pretend the second one is free.
Stay single phase at 7.44 kWp. You offset what you can, keep the job simple, and avoid a separate application to TNB. For most households whose usage sits under about 800 kWh a month, this covers the daytime load comfortably.
Upgrade to three phase. TNB charges separately for this and it is a distinct piece of work from the solar installation. We do not publish a figure for that upgrade, because we do not have one we can stand behind. Many customers ask us what it costs; the honest answer is that it depends on your existing supply and distance to the nearest three-phase source, and TNB quotes it per premise. Ask us and we will get it confirmed rather than guess.
The other cap: exceeding the phase limit
Going above your phase ceiling is not simply forbidden — it needs TNB CCC approval plus a RM1,000 fee, and a wait. For a domestic customer that is rarely worth it. It matters mostly for larger commercial premises, where the limit is set by Maximum Demand rather than a flat kWac figure.
Why oversizing hurts under Solar ATAP
It is tempting to fit the biggest system your phase allows. Under ATAP that can cost you money.
Electricity you use as it is generated saves the full avoided rate — RM0.4443/kWh on the standard domestic tier. Electricity you export earns the Energy Charge only, RM0.2703/kWh. And any credit you do not use within the billing period is forfeited at the end of that month. It does not roll forward.
So a system that generates well beyond what you consume is selling the surplus at a lower rate, and losing whatever is left over entirely. The right size is one where generation lands close to your usage — which is why we ask for your bill, and whether anyone is home during the day, before recommending anything.
What to send us
Three things and we can size your system properly: your average monthly TNB bill (or better, the last three bills), your supply phase, and whether anyone is usually home during the day. The third can change the answer noticeably, and almost nobody asks it.
